I purchased my truck as a demonstrator so it already had 5300 miles on her. After driving 700 miles mixed with about 60% city and 40% highway, I'm averaging right at 26.5 mpg. The EVIC was very accurate on the first tank of fuel showing 26.5mpg compared with 26.4mpg calculated. I'm averaging close to 27 on the EVIC now with the second tank of fuel. I would say I've taken it fairly easy over the 700 miles with driving aggressively only a few times. It definitely sucks down some fuel if you get on it regularly and I could see dropping below 20mpg in the city if I drove it hard.
I have a 2wd Laramie Longhorn with 3.55 gears.